Advanced fire-resistant forms of activated carbon and methods of adsorbing and separating gases using same

ABSTRACT

Advanced, fire-resistant activated carbon compositions useful in adsorbing gases; and having vastly improved fire resistance are provided, and methods for synthesizing the compositions are also provided. The advanced compositions have high gas adsorption capacities and rapid adsorption kinetics (comparable to commercially-available activated carbon), without having any intrinsic fire hazard. They also have superior performance to Mordenites in both adsorption capacities and kinetics. In addition, the advanced compositions do not pose the fibrous inhalation hazard that exists with use of Mordenites. The fire-resistant compositions combine activated carbon mixed with one or more hydrated and/or carbonate-containing minerals that release H 2 O and/or CO 2  when heated. This effect raises the spontaneous ignition temperature to over 500° C. in most examples, and over 800° C. in some examples. Also provided are methods for removing and/or separating target gases, such as Krypton or Argon, from a gas stream by using such advanced activated carbons.

STATEMENT OF GOVERNMENT INTEREST

This invention was developed under Contract DE-AC04-94AL85000 betweenSandia Corporation and the U.S. Department of Energy. The U.S.Government has certain rights in the invention.

FIELD OF THE INVENTION

The invention relates to advanced, fire-resistant forms of activatedcarbon that contain hydrated and/or carbonate-containing minerals (e.g.,hydrated magnesium carbonates, hydrated magnesium chloride hydroxides,hydrated magnesium silicates, hydrated calcium and sodium citrates,calcium carbonate, or sodium bicarbonate); and methods of using suchadvanced activated carbon formulations to adsorb and/or to separategases in a gas stream.

BACKGROUND OF THE INVENTION

Reprocessing of spent nuclear fuel, e.g. PUREX™ reprocessing, generatesnuclear off-gas that contains several radioactive isotopes, includinggaseous ¹²⁹I and noble gases ⁸⁵Kr and ¹³³Xe. Entrapping noble gasnuclides for permanent disposal is technically challenging because theyare chemically inert. Only very aggressive agents, such as fluorine, canform compounds with noble gas nuclides. The half-lives of ⁸⁵Kr and ¹³³Xeare 10.7 years and 5.3 days, respectively. As the half-life of ¹³³Xe issufficiently short, the Xe activity would be negligible if the spentfuel were stored for several months before reprocessing. Therefore, theseparation and capture of ⁸⁵Kr becomes a key issue in trappingradioactive noble gases.

Several methods have been proposed for trapping radioactive noble gasstreams from the off-gas. These methods include cryogenic distillationand membrane separation. The cryogenic distillation process is wellunderstood. However, the drawbacks include higher operating cost and thepotential for fire hazard because of ozone accumulation. The membraneseparation process also has high operating cost and low throughput, orefficiency.

Activated carbon is one known adsorbent, which has a high capacity toadsorb noble gases. In addition, activated carbon is relativelyinexpensive in comparison to the cryogenic and membrane separationmethods. Activated carbon, however, poses a significant fire hazard. Fortrapping of noble gases, and particularly trapping of radioactive ⁸⁵Kr,an activated carbon adsorbent that does not pose a significant firehazard would provide economical and efficient permanent disposal orlong-term storage options. Such an activated carbon would therefore bedesirable.

In addition, activated carbon adsorbents that do not pose a significantfire risk would be desirable in other industries. For instance, in thechemical and petrochemical industries, activated carbon adsorbers areused to control emissions of solvents and other volatile organiccompounds (VOC's) from process streams, off-gases and tank ventings. Thevolatile organic compounds associated with petrochemical industriesinclude, for example and not limited to, benzene, toluene, xylene (o-,p-, m-isomers), petroleum distillate fractions (naphtha),2-butoxyethanol, and ethyl benzene.

In the fields of environmental engineering, nuclear, military, andspecialist extraction, activated carbon is also used to remove VOC's andother chemicals. For example, aliphatic, aromatic, unsaturates andalicyclics hydrocarbons and other pollutants are present in theatmosphere of submarines and are removed by activated carbon beds.Despite their use in these industries, the fire risk posed by theactivated carbon is of great concern and there have been a number offire accidents related to activated carbon ignition. Thus, an advanced,fire-resistant activated carbon material would be desirable in suchother industries as well.

SUMMARY OF THE INVENTION

The invention provides advanced, fire-resistant forms of activatedcarbon having improved fire resistance, methods of making same, andmethods of using same to adsorb and/or separate gases.

A first aspect of the invention provides an advanced activated carboncomprising between 5 and 95 wt % of one or more hydrated and/orcarbonate-containing mineral wherein the mineral contains between 15 and16 wt % water and between 95 and 5 wt % activated carbon.

Certain embodiments of the invention provide an advanced activatedcarbon including between 15 and 40 wt % hydrated magnesite, wherein thehydrated magnesite contains between 15 and 16 wt % water and between 60and 85 wt % activated carbon.

One specific embodiment of the invention provides an advanced activatedcarbon including between 22 and 27 wt % hydrated magnesite and between78 and 73 wt % activated carbon. In another embodiment of the invention,the advanced activated carbon includes between 33 and 35 wt % hydratedmagnesite and between 67 and 65 wt % activated carbon.

A second aspect of the invention provides an advanced activated carbonincluding between 30 and 50 wt % hydrated sepiolite, wherein thehydrated sepiolite contains between 16 and 17 wt % water; and between 70and 50 wt % activated carbon.

One specific embodiment of the invention provides an advanced activatedcarbon has between 44 and 46 wt % hydrated sepiolite and between 56 and54 wt % activated carbon.

A third aspect of the invention provides an advanced activated carbonincluding between 30 and 45 wt % hydrated nesquehonite, wherein thehydrated nesquehonite contains between 39 and 40 wt % water; and between70 and 55 wt % activated carbon.

In one embodiment of the invention, the advanced activated carbon hasbetween 44 and 46 wt % hydrated nesquehonite and between 56 and 54 wt %activated carbon. In another embodiment of the invention, the advancedactivated carbon has between 38 and 40 wt % hydrated nesquehonite andbetween 62 and 60 wt % activated carbon.

A fourth aspect of the invention provides an advanced activated carbonincluding between 45 and 60 wt % hydrated calcium citrate tribasic,wherein the hydrated calcium citrate tribasic contains between 12 and 13wt % water; and between 55 and 40 wt % activated carbon.

In one embodiment of the invention, the advanced activated carbon hasbetween 53 and 55 wt % hydrated calcium citrate tribasic and between 47and 45 wt % activated carbon.

In specific embodiments of the invention, the advanced activated carbonhas a krypton adsorption rate constant at 25° C. of equal to or greaterthan 0.35 mg/g min⁻¹.

A fifth aspect of the invention provides an advanced activated carbonincluding between 40 and 70 wt % sodium bicarbonate and between 60 and30 wt % activated carbon.

A sixth aspect of the invention provides a method of removing a targetgas from a gas stream including contacting the gas stream with anadvanced activated carbon selected from the group consisting of anadvanced activated carbon having between 15 and 40 wt % hydratedmagnesite and between 60 and 85 wt % activated carbon; an advancedactivated carbon having between 30 and 50 wt % hydrated sepiolite andbetween 70 and 50 wt % activated carbon; an advanced activated carbonhaving between 30 and 45 wt % hydrated nesquehonite and between 70 and55 wt % activated carbon; and an advanced activated carbon havingbetween 45 and 60 wt % hydrated calcium citrate tribasic and between 55and 40 wt % activated carbon.

In one embodiment of the inventive method the contacting occurs at roomtemperature.

In another embodiment of the inventive method, structural water and/orCO₂ are released from the advanced activated carbon.

In yet another embodiment of the inventive method, the target gas isselected from the group of noble gases, ¹²⁹I gas, volatile organiccompounds, and combinations thereof.

Yet another embodiment of the invention provides a method for separatinggasses comprising contacting a gaseous mixture with the inventiveadvanced activated carbon.

Yet another embodiment of the invention provides a method for making theinventive advanced activated carbon by first separately weighing out thedesired amounts of the one or more hydrated and/or carbonated containingminerals and activated carbon and then mixing such amounts by mechanicalmixing.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form that is exemplary; it being understood, however, thatthis invention is not limited to the precise arrangements andinstrumentalities shown.

FIG. 1 is graph generated from thermogravimetric analysis ofhydromagnesite (e.g., Mg₅[CO₃]₄[OH]₂.4H₂O), used to produce InventiveExamples 1 and 2, illustrating the weight loss as a function of time andtemperature, wherein the solid line indicates the weight loss and thedotted line shows the temperature ramp profile;

FIG. 2 illustrates the adsorption curve of Kr at 680 torrs ontoInventive Example 6 in which TG means thermal gravimetric and Temp meanstemperature and wherein the solid line indicates the weight loss and thedotted line shows the temperature ramp profile;

FIG. 3 is a graph illustrating the amount of Kr adsorbed onto InventiveExample 5 (mg Kr/g Inventive Example 5) at room temperature as afunction of time;

FIG. 4 is a graph illustrating the amount of Kr adsorbed onto InventiveExample 5 (mg Kr/g Inventive Example 5) at room temperature as a linearfunction of time, from which the rate constant can be obtained from theslope, wherein the solid line is a fitted linear function and the opencircles represent experimentally measured points;

FIG. 5 is a graph illustrating the XRD results of hydrated magnesite andnesquehonite used in the Examples herein;

FIG. 6 illustrates the DTA and TGA results for AAAC where the heavysolid line indicates the TGA curve, the heavy broken line indicates theDTA curve, and the arrowed line indicates the spontaneous ignitiontemperature;

FIG. 7 illustrates the DTA and TGA results for Inventive Example 1 wherethe heavy solid line indicates the TGA curve, the heavy broken lineindicates the DTA curve, and the arrowed line indicates the spontaneousignition temperature;

FIG. 8 illustrates the DTA and TGA results for Inventive Example 2 wherethe heavy solid line indicates the TGA curve, the heavy broken lineindicates the DTA curve, and the arrowed line indicates the spontaneousignition temperature;

FIG. 9 illustrates the DTA and TGA results for Inventive Example 3 wherethe heavy solid line indicates the TGA curve, the heavy broken lineindicates the DTA curve, and the arrowed line indicates the spontaneousignition temperature;

FIG. 10 illustrates the DTA and TGA results for Inventive Example 4where the heavy solid line indicates the TGA curve, the heavy brokenline indicates the DTA curve, and the arrowed line indicates thespontaneous ignition temperature;

FIG. 11 illustrates the DTA and TGA results for Inventive Example 5where the heavy solid line indicates the TGA curve, the heavy brokenline indicates the DTA curve, and the arrowed line indicates thespontaneous ignition temperature;

FIG. 12 illustrates the DTA and TGA results for Inventive Example 6where the heavy solid line indicates the TGA curve, the heavy brokenline indicates the DTA curve, and the arrowed line indicates thespontaneous ignition temperature;

FIG. 13 illustrates the DTA and TGA results for Inventive Example 7where the heavy solid line indicates the TGA curve, the heavy brokenline indicates the DTA curve, and the arrowed line indicates thespontaneous ignition temperature;

FIG. 14 illustrates the DTA and TGA results for Inventive Example 8where the heavy solid line indicates the TGA curve, the heavy brokenline indicates the DTA curve, and the arrowed line indicates thespontaneous ignition temperature;

FIG. 15 illustrates the DTA and TGA results for Inventive Example 9where the heavy solid line indicates the TGA curve, the heavy brokenline indicates the DTA curve, and the arrowed line indicates thespontaneous ignition temperature;

FIG. 16 illustrates the DTA and TGA results for Inventive Example 10where the heavy solid line indicates the TGA curve, the heavy brokenline indicates the DTA curve, and the arrowed line indicates thespontaneous ignition temperature;

FIG. 17 illustrates the DTA and TGA results for Inventive Example 11where the heavy solid line indicates the TGA curve, the heavy brokenline indicates the DTA curve, and the arrowed line indicates thespontaneous ignition temperature; and

FIG. 18 illustrates the DTA and TGA results for Inventive Example 12where the heavy solid line indicates the TGA curve, the heavy brokenline indicates the DTA curve, and the arrowed line indicates thespontaneous ignition temperature.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention relates to advanced, fire-resistant forms of activatedcarbon that contain hydrated or carbonated minerals and/or The inventionfurther provides methods of using such advanced activated carbonformulations to adsorb and/or separate gases.

As used herein the terms “hydrated magnesite” and “hydromagnesite” areinterchangeable.

The term “one or more hydrated and/or carbonate-containing mineral” asused herein means one or more hydrated minerals, one or morecarbonate-containing minerals, or a combination of one or more hydratedminerals and one or more carbonate-containing minerals.

Some advanced forms of activated carbon, according to the invention,comprise a mixture of activated carbon and a fire-suppressing additiveor agent. The fire-suppressing additive or agent can be a material thatreleases water, or carbon dioxide, or both water and carbon dioxide,when heated. The fire-suppressing additive or agent can be mechanicallymixed with, combined with, incorporated into, impregnated into, adsorbedonto, and/or bonded or joined to the activated carbon material.

In one embodiment, the ingredients (the activated carbon and the one ormore fire-suppressing additives) for making up an advanced activatedcarbon composition are first manually mixed. Then, the manually-mixedmaterial is loaded into a McCrone Micronising Mill (mixer mill, GlenCreston Limited), and ground to a sub-micron size. This produces ahomogeneous mixture (agglomeration) of sub-micron size particles,without any observable phase separation between the activated carbon andfire-suppressing additive(s). Visually, the homogeneous mixture ofsub-micron size particles typically appears uniformly black. Someadvanced forms of activated carbon according to the invention comprisean activated carbon and a nano-structured hydrated metal carbonate ormetal silicate solid phase additive or agent, wherein the hydrated metalcarbonate or metal silicate solid is capable of releasing structuralwater at elevated temperatures (e.g., less than or equal to 500° C.) andcan also be capable of producing other endothermic reactions (e.g., upto 900° C.), e.g., carbon dioxide.

The fire-suppressing agents or additives according to the invention maybe a hydrated metal carbonate and/or a hydrated metal silicate.

In some embodiments, the advanced activated carbon composition cancomprise a mixture of activated carbon and at least one carbondioxide-evolvable additive, wherein the carbon dioxide-evolvableadditive evolves (i.e., releases) carbon dioxide gas when thecomposition is heated above 300° C. The carbon dioxide-evolvableadditive can additionally comprise structural water (e.g., in a hydratedstructural form), wherein water vapor is released when the compositionis heated above 100° C.

Some examples of carbon dioxide-evolvable additives, according to theinvention, include: hydromagnesite, hydrated nesquehonite, hydratedcalcium citrate tribasic, sodium citrate dihydrate, magnesium chloridehydroxide hydrate, sodium bicarbonate, and calcium carbonate, andcombinations thereof.

In other embodiments, an advanced activated carbon composition cancomprise a mixture of activated carbon and at least one water-evolvableadditive, wherein the water-evolvable additive evolves (i.e., releases)water vapor when the composition is heated above 100° C. Some examplesof water-evolvable additives, according to the invention, include:hydromagnesite, hydrated sepiolite, hydrated nesquehonite, hydratedcalcium citrate tribasic, sodium citrate dihydrate, magnesium chloridehydroxide hydrate, and combinations thereof.

In other embodiments, an advanced activated carbon composition cancomprise a mixture of activated carbon and at least one water-evolvableand at least one carbon dioxide-evolvable additive, wherein the watervapor evolves when the composition is heated above 100° C. and carbondioxide gas evolves when the composition is heated above 300° C.

Hydrated metal carbonates useful in some embodiments of the inventionmay be: hydromagnesite (e.g., Mg₅[CO₃]₄[OH]₂.4H₂O), hydratednesquehonite (e.g., MgCO₃.3H₂O), hydrated calcium citrate tribasic(e.g., Ca₃(C₆H₅O₇)₂.4H₂O), sodium citrate dihydrate (e.g.,Na₃(C₆H₅O₇).2H₂O), magnesium chloride hydroxide hydrate (e.g.,Mg₃(OH)₅Cl.4H₂O) or (e.g., Mg₂(OH)₃Cl.4H₂O), or any combination thereof.

Hydrated metal silicates useful in some embodiments of the invention maybe, for example, hydrated sepiolite (e.g., Mg₄Si₆O₁₅(OH)₂.6H₂O).

The fire-suppressing agents or additives according to the invention maycomprise carbonates, such as calcium carbonate or sodium bicarbonate,and combinations thereof.

Activated carbons useful in embodiments of the invention include,without limitation, commercially-available activated carbon, forexample, activated carbon available from Alfar Aesar™.

The chemical formulas shown in Table 1, and elsewhere, show specificexamples of a specific amount (i.e., degree) of hydration. For example,an example of the formula for hydromagnesite is shown as“Mg₅[CO₃]₄[OH]₂.4H₂O” in Inventive Example 1. However, in real minerals,the degree of hydration is variable, depending on the processingconditions, amount of impurities, etc. Therefore, when we state aparticular mineral (e.g., hydromagnesite), we define that term toinclude a realistic range in the degree (amount) of hydration. Forexample, we define the term “hydromagnesite” to include a range inhydration states, (Mg₅[CO₃]₄[OH]₂.NH₂O), where N can range from 0.5 to11. In other words, the term “hydromagnesite” is broadly defined hereinto include similar phases and their solid solutions with other degreesof hydration than just N=4.

Other examples of suitable hydrated carbonate-containing minerals, whichcan be combined with activated carbon to make an advanced activatedcarbon composition according to the present invention, include:dypingite (e.g., Mg₅[CO₃]₄[OH]₂.5H₂O), giorgiosite (e.g.,Mg₅[CO₃]₄[OH]₂.5H₂O), widgiemoolthalite (e.g., [Ni,Mg]₅[CO₃]₄[OH]₂.4.5H₂O), pokrovskite (e.g., Mg₂[CO₃][OH]₂.0.5 H₂O),coalingite (e.g., Mg₁₀Fe₂[CO₃][OH]₂₄.2H₂O), brugnatellite (e.g.,Mg₆Fe[CO₃][OH]₁₃.4H₂O), artinite (e.g., Mg₂[CO₃][OH]₂.3H₂O),hydrotalcite (e.g., Mg₆Al₂[CO₃][OH]₁₆.4H₂O), manasseite (e.g.,Mg₆Al₂[CO₃][OH]₁₆.4H₂O), chlorartinite (e.g., Mg₂[CO₃]Cl[OH].3H₂O),barbertonite (e.g., Mg₆Cr₂[CO₃][OH]₁₆.4H₂O), stichtite (e.g.,Mg6Cr₂[CO₃][OH]₁₆.4H₂O), desautelsite (e.g., Mg₆Mn₂[CO₃][OH]₁₆.4H₂O),pyroaurite (e.g., Mg₆Fe₂[CO₃][OH]₁₆.4H₂O), sjogrenite (e.g.,Mg₆Fe₂[CO₃][OH]₁₆.4H₂O), sergeevite (e.g.,Mg₁₁Ca₂[CO₃]₉[HCO₃]₄[OH]₄.6H₂O), mountkeithite (e.g., [Mg, Ni]₁₁[Fe,Cr]₃[SO4, CO₃]_(3.5)[OH]₂₄.11H₂O), and baylissite (e.g.,K₂Mg[CO₃]₂.4H₂O), and combinations thereof.

In some embodiments of the invention the hydrated magnesite(hydromagnesite) is present in the advanced activated carbon in anamount in the range of 15 to 40 wt %, alternatively between 20 and 36 wt%, alternatively between 22 and 30 wt %, alternatively between 30 and 37wt %, or alternatively between 33 and 35 wt %.

In some embodiments of the invention the hydrated nesquehonite ispresent in the advanced activated carbon in an amount in the range of 30to 50 wt %, alternatively between 35 and 48 wt %, alternatively between38 and 40 wt %, alternatively between 40 and 46 wt %, or alternativelybetween 44 and 46 wt %.

Hydromagnesite can be synthesized by first mixing a 1.0 M Na₂CO₃solution with a 1 M MgCl₂ solution at 21° C. Then, after one day, theprecipitates were filtered out with vacuum filtration. The filteredmaterial was then dried at 60° C. for one day. In a similar fashion,hydrated nesquehonite can be synthesized by first mixing a 1.4 M NH₄HCO₃solution with a 2.0 M MgCl₂ solution at 50° C. on a hot plate withstirring for 2 hours. Then, the solution was put on a lab bench at 21°C. for two days. The precipitates were then filtered out with vacuumfiltration. The filtered precipitates were dried at 21° C. for one day.The synthesized hydromagnesite and nesquehonite have well-defined XRDpatterns, as shown in FIG. 5. The top curve in FIG. 5 is fornesquehonite and the bottom curve is for hydromagnesite.

The final composition, especially for the mixing product produced duringthe synthesizing hydromagnesite in the presence of activated carbon, canbe described as an agglomerate or agglomeration.

In another embodiment of a method of making the inventive compositions,the method steps can comprise the following. First, 100 mL of 1 M Na₂CO₃was prepared and placed into a beaker with a stir bar. Then, desiredamounts of activated carbon were put into the beaker to make a slurry.After that, 100 mL of 1 m MgCl₂ solution was added into the beaker, andhydromagnesite started to precipitate. The stir bar continuously stirredthe solution/slurry for the entire period of synthesis. Then, the solidsare filtered out from the liquid, and the solids dried. Finally, thesolids are mechanically ground/milled to a sub-micron size, whichproduces the final advanced activated carbon composition. In thisembodiment, the activated carbon is added to the beaker before thehydromagnesite is precipitated out. In this case, we call this processas a “chemical precipitation mixing” method. In contrast, if thisactivated carbon was added to the beaker after the hydromagnesite hadbeen precipitated out, then we would call that process a simple“mechanical mixing” process.

A preferred process is to add the activated carbon to the beaker beforethe MgCl₂ solution is added into the beaker to precipitatehydromagnesite (or other hydrated mineral).

The chemical precipitation mixing method described above can be used toprepare any of the inventive examples and embodiments listed in Table 1,as well as for any of the other hydrated and/or carbonate mineralslisted in this application.

In some embodiments of the invention the hydrated sepiolite is presentin the advanced activated carbon in an amount in the range of 30 to 50wt %, alternatively between 35 and 48 wt %, alternatively between 40 and47 wt %, or alternatively between 44 and 46 wt %.

In some embodiments of the invention the hydrated calcium citratetribasic is present in the advanced activated carbon in an amount in therange of 45 to 60 wt %, alternatively between 48 and 58 wt %,alternatively between 50 and 56 wt %, or alternatively between 53 and 55wt %.

In some embodiments of the invention the sodium bicarbonate is presentin the advanced activated carbon in an amount in the range of 40 to 75wt %, alternatively between 45 and 70 wt %, or alternatively between 48and 68 wt %.

Some advanced activated carbons of the invention can have a Kryptonadsorption rate constant at 25° C. of equal to or greater than 0.35 mg/gmin⁻¹, alternatively greater than 0.48 mg/g min⁻¹, alternatively greaterthan 0.65 mg/g min⁻¹, or alternatively greater than 0.73 mg/g min⁻¹.

The method of removing a target gas from a gas stream of the inventioncomprises contacting the gas stream with one or more of the advancedactivated carbon described herein. By way of example but not by way oflimitation, such advanced activated carbon may be selected from thegroup consisting of an advanced activated carbon comprising between 15and 40 wt % hydrated magnesite; an advanced activated carbon comprisingbetween 30 and 50 wt % hydrated sepiolite; an advanced activated carboncomprising between 30 and 45 wt % hydrated nesquehonite; an advancedactivated carbon comprising between 45 and 60 wt % hydrated calciumcitrate tribasic; an advanced activated carbon comprising between 40 and70 wt % sodium bicarbonate, and any combination thereof.

In some embodiments of the inventive method, the contacting with a gasstream occurs at a temperatures between room temperature and a measuredignition temperature, alternatively between 15 and 30° C., alternativelybetween 20 and 27° C., alternatively between 25 and 250° C.,alternatively between 20 and 200° C., or alternatively between 50 and150° C.

In some embodiments of the inventive method, structural water and/or CO₂are released from the advanced activated carbon when heated.

In some embodiments, the hydrated magnesium carbonate is hydratednesquehonite, and up to 40 wt % water based on the total weight of thehydrated nesquehonite is released during the contacting; alternatively,up to 30 wt % water is released; alternatively up to 35 wt % water isreleased.

In some embodiments, the hydrated magnesium carbonate is hydromagnesiteand up to 16 wt % water based on the total weight of the hydromagnesiteis released during the contacting; alternatively, up to 15 wt % water isreleased; alternatively up to 13 wt % water is released.

In some embodiments, the hydrated magnesium silicate is hydratedsepiolite and up to 18 wt % water based on the total weight of thehydrated sepiolite is released during the contacting; alternatively, upto 17 wt % water is released; alternatively up to 15 wt % water isreleased.

In some embodiments, the advanced activated carbon comprises hydratedcalcium citrate tribasic and up to 13 wt % water based on the totalweight of the hydrated calcium citrate tribasic is released during thecontacting; alternatively, up to 12 wt % water is released;alternatively up to 10 wt % water is released.

In some embodiments of the inventive method, the target gas is selectedfrom the group of noble gases, ¹²⁸I gas, volatile organic compounds, andcombinations thereof.

Without being bound by any particular theory, it is believed that theinventive advanced forms of activated carbon substantially decrease oreliminate the risk of fire due to the ability to release structuralwater when heated. As the ignition temperature of standard activatedcarbon is 250° C. (and exothermic oxidative reactions of activatedcarbon occur at temperature as low as 200° C.) the advanced forms ofactivated carbon contain fire-suppressing agents or additives that canrelease structural water well below 200° C. (the exothermic oxidativereaction temperature of activated carbon) if they are heated duringadsorption or separation processes, or during material storage. Thereleased water then can capture heat released, because water has a largeheat capacity, thereby preventing the temperature from reaching thetemperature required for the oxidative reactions of the activatedcarbon. At higher temperatures, the inert gas CO₂ is released, whichacts as a diluent to lower the partial pressure of oxygen in thesurrounding environment; acting further to suppress the process of tireignition and burning.

Any numerical range recited herein, includes all values from the lowervalue and the upper value, in increments of one unit, provided thatthere is a separation of at least two units between any lower value andany higher value. As an example, if it is stated that a compositional,physical or other property, such as, for example, molecular weight, isfrom 100 to 1,000, it is intended that all individual values, such as100, 101, 102, etc., and sub ranges, such as 100 to 144, 155 to 170, 197to 200, etc., are expressly enumerated in this specification. For rangescontaining values which are less than one, or containing fractionalnumbers greater than one (e.g., 1.1, 1.5, etc.), one unit is consideredto be 0.0001, 0.001, 0.01 or 0.1, as appropriate. For ranges containingsingle digit numbers less than ten (e.g., 1 to 5), one unit is typicallyconsidered to be 0.1. These are only examples of what is specificallyintended, and all possible combinations of numerical values between thelowest value and the highest value enumerated, are to be considered tobe expressly stated in this application.

The above description and examples that follow illustrate, but do notlimit, various aspects or embodiments of this invention.

EXAMPLES Methods and Materials

Each of the advanced activated carbons of embodiments of the inventionwere prepared by first separately weighing out the desired masses of theone or more hydrated and/or carbonated containing minerals and activatedcarbon and then mixing such amounts by mechanical mixing (e.g., by usinga mortar and pestle to grind the ingredients by hand).

Gas adsorption measurements were made gravimetrically using the vacuummicrobalance in a Netzsch STA 409 thermal gravimetric analyzer (TGA)with differential scanning calorimeter (DSC) and Differential ThermalAnalyzer (DTA). The masses of each advanced activated carbon sample werefirst measured with a Mettler Toledo AT 261 Delta Range balance with aprecision to 0.0001 g (0.1 mg). The advanced activated carbon samplemass was usually about 100 mg. The advanced activated carbon sample wasthen loaded into a small crucible in the TGA, the system purged tovacuum, followed by a backfill of a noble gas to the desired pressure.Specifically, the advanced activated carbon samples were analyzed foradsorption of Ar and Kr gases, each at 0.2 to 0.9 atmospheric pressures.The advanced activated carbon samples were then analyzed to determinethe amount of noble gas adsorption by using an automatedtime/temperature profile. The time/temperature profile was as follows:(1) heating to 90° C.; (2) maintaining at 90° C. for two hours(desorption step) in which desorbed gas was purged out of the system viaan exhaust tube; (3) cooling to room temperature with noble gas beingbackfilled; and (4) maintaining at room temperature for two hours(adsorption step). The amount of adsorbed noble gas on an advancedactivated carbon sample was determined by the weight difference betweenan activated carbon sample analysis from an instrumental blank. Theinstrumental blank was made by employing the same, but empty crucible,which was used for the activated carbon sample analyses. Thetime/temperature profile for the instrumental blank and a sampleanalysis were the same. The amounts of absorbed noble gas are calculatedbased on the mass of noble gas absorbed in the adsorption step, as thedesorption step serves as a zero background. The TGA was subjected tothe same time/temperature profile and the weight gain subtracted fromthe instrumental blank in order to eliminate any effect of weight gainby the TGA itself.

The advanced activated carbon compositions were characterized usingX-ray diffractometer (“XRD”) (Burker D8 Advance).

Table 1 provides the chemical composition of Inventive Examples 1-6.Table 2 provides the chemical composition of Comparative Examples 1-2.

TABLE 1 Weight percentage of Weight additives (wt. % variationspercentage of Materials based on multiple samples) Activated CarbonInventive Example 1 22.03-26.37 of Balance hydromagnesite (e.g.,Mg₅[CO₃]₄[OH]₂•4H₂O) Inventive Example 2 33.21-34.38 of Balancehydromagnesite [e.g., Mg₅[CO₃]₄[OH]₂•4H₂O) Inventive Example 3 44.1-45.7of hydrated Balance sepiolite [e.g., Mg₄Si₆O₁₅(OH)₂•6H₂O) InventiveExample 4 45.0 of hydrated Balance nesquehonite (e.g., MgCO₃•3H₂O)Inventive Example 5 38.8-39.59 of hydrated Balance nesquehonite (e.g.,MgCO₃•3H₂O) Inventive Example 6 54.0 of hydrated calcium Balance citratetribasic [e.g., Ca₃(C₆H₅O₇)₂•4H₂O] Inventive Example 7 66.0 of sodiumbicarbonate Balance [NaHCO₃] Inventive Example 8 49.1 of sodiumbicarbonate Balance [NaHCO₃] Inventive Example 9 48.5 of calciumcarbonate Balance [CaCO₃] Inventive Example 10 51.0 of sodium citrateBalance dihydrate [e.g., Na₃(C₆H₅O₇)•2H₂O] Inventive Example 11 47.2 ofsodium bicarbonate Balance [Na₃HCO₃] Inventive Example 12 49.2 ofhydrated magnesium Balance chloride hydroxide hydrate [e.g.,Mg₃(OH)₅Cl•2H₂O]

TABLE 2 Composition Comparative Example 1 NH₄-Mordenite (“Mordenite-N”)Comparative Example 2 Na-Mordenite (“Mordenite-A”)

FIG. 2 illustrates the adsorption curve of Kr at 680 torrs ontoInventive Example 6 in which TG means thermal gravimetric and Temp meanstemperature and wherein the solid line indicates the weight loss and thedotted line shows the temperature ramp profile.

FIG. 3 is a graph illustrating the amount of Kr adsorbed onto InventiveExample 5 (mg Kr/g Inventive Example 5) at room temperature as afunction of time.

Table 3 provides the results of analyses of adsorption amounts of Ar andKr gases on each of the Inventive and Comparative Examples andcommercial activated carbon. It is clear that the gas adsorptioncapacities of the inventive advanced forms of activated carbon arecomparable to those of commercially-available activated carbon; and aresuperior to those of Na-mordenite and to NH₄-mordenite.

TABLE 3 Wt % of solid phase additive containing Ar Kr structural waterin the adsorbed, adsorbed, advanced forms of Sample wt % wt % activatedcarbon Inventive Example 1 0.42 ± 0.06 3.01 22.0 (Kr experiment); 26.4(Ar experiment) Inventive Example 2 0.37 ± 0.01 2.51 33.2 (Krexperiment); 33.9 (Ar experiment) Inventive Example 3 — 2.56 44.1Inventive Example 4 — 1.63 45.0 Inventive Example 5 — 2.69 38.8Inventive Example 6 — 2.06 54.0 DARCO activated carbon 0.72 3.60 N/AAlfa Aesar 0.50 Not N/A activated carbon Tested Comparative Example 10.27 1.74 N/A Comparative Example 2 0.12 1.31 N/A

Table 4 provides the weight percentage of structural water released fromthe hydrated solid phase additives as a function of temperature. Noticethat the hydromagnesite and hydrated nesquehonite additives release morethan 15 wt % of structural water below 300° C. In addition, these twoagents release CO₂ above 350° C. (see, e.g., FIG. 1). Notice also thatthe total amount of water released measured experimentally agrees wellwith the theoretical water content in 3 out of the 4 additives tested inTable 4.

TABLE 4 Theoret- Water released ical (in wt %) as water a function ofcontents, temperature Additive wt % below 300° C. Used in:hydromagnesite (e.g., 15.4 5.14 (125° C.), 2.84 InventiveMg₅[CO₃]₄[OH]₂•4H₂O) (125° C.-160° C.), Examples 8.97 (160° C.-250° C.)1 and 2 Total released = 16.95 wt % hydrated sepiolite [e.g., 16.7 2.34(130° C.), 0.95 Inventive Mg₄Si₆O₁₅(OH)₂•6H₂O] (130° C.-250° C.) ExampleTotal released = 3 3.29 wt % hydrated nesquehonite 39.1 17.98 (150° C.),10.47 Inventive (e.g., MgCO₃•3H₂O]) (150° C.-175° C.), 6.12 Examples(175° C.-225° C.) 4 and 5 Total released = 34.57 wt % hydrated calcium12.6 3.07 (105° C.), 7.79 Inventive citrate tribasic [e.g., (105°C.-172° C.) Example Ca₃(C₆H₅O₇)₂•4H₂O] Total released = 6 10.86 wt %

FIG. 1 is graph generated from thermogravimetric analysis ofhydromagnesite (e.g., Mg₅[CO₃]₄[OH]₂.4H₂O), used to produce InventiveExamples 1 and 2, illustrating the weight loss as a function of time andtemperature up to 400° C., wherein the solid line indicates the weightloss and the dotted line shows the temperature ramp profile. Thetheoretical structural water (H₂O) content in the solid sample is 15.4wt %. Upon heating, 5.14 wt % of water is released at 125° C. Then, 2.84wt % is released between 125° C. and 160° C. Finally, 8.97 wt % of wateris released between 160° C. and 250° C. In the temperature range from250° C. to about 350° C., water contained in hydroxyl groups (i.e., OH)is released. At temperatures higher than 350° C., 25.1 wt % of CO₂ isreleased.

FIG. 4 is a graph illustrating the amount of Kr adsorbed onto InventiveExample 5 (mg Kr/g Inventive Example 5) at room temperature as a linearfunction of time, from which the rate constant can be obtained from theslope, wherein the solid line is a fitted linear function and the opencircles represent experimentally measured points. The initial linearportion of adsorption curves is used to obtain adsorption rateconstants, as illustrated in FIGS. 3 and 4.

Table 5 provides the gas adsorption rate constants at 680 torr and 25°C. for each of the Inventive and Comparative Examples and DARCOactivated carbon. The results in Table 5 indicate that the inventiveadvanced forms of fire-resistant activated carbon have gas adsorptionrate constants higher than those of both the Na-mordenite and toNH₄-mordenites (which have been considered for adsorption of radioactivenoble gases, and are comparable to those of activated carbon).

TABLE 5 Noble gas Adsorption rate constant Material adsorbed (k_(Ar) ork_(Kr)), mg/g min⁻¹ Mordenite-A Argon 4.10 × 10⁻² (Ca, Na₂,K₂)Al₂Si₁₀O₂₄•7H₂O Mordenite-A Krypton 2.53 × 10⁻¹ k_(Kr)/k_(Ar) 6.17Mordenite-N Argon 8.84 × 10⁻² (Ca, Na₂, K₂)Al₂Si₁₀O₂₄•7H₂O Mordenite-NKrypton 5.00 × 10⁻¹ k_(Kr)/k_(Ar) 5.66 Inventive Ex. 1 Argon 2.59 × 10⁻¹Inventive Ex. 1 Krypton 7.46 × 10⁻¹ Inventive Ex. 1 2.88 k_(Kr)/k_(Ar)Inventive Ex. 2 Argon 1.52 × 10⁻¹ Inventive Ex. 2 Krypton 6.67 × 10⁻¹Inventive Ex. 2 4.39 k_(Kr)/k_(Ar) Inventive Ex. 3 Krypton 6.41 × 10⁻¹Inventive Ex. 4 Krypton 3.86 × 10⁻¹ Inventive Ex. 5 Argon 8.13 × 10⁻²Inventive Ex. 5 Krypton 6.62 × 10⁻¹ Inventive Ex. 5 8.14 k_(Kr)/k_(Ar)Inventive Ex. 6 Krypton 4.94 × 10⁻¹ DARCO activated Argon 3.66 × 10⁻¹carbon DARCO activated Krypton 9.95 × 10⁻¹ carbon DARCO activated 2.72carbon k_(Kr)/k_(Ar)

The K_(Kr)/K_(ar) gas adsorption selectivity ratio is defined as theratio of the gas adsorption rate constant for krypton divided by the gasadsorption rate constant for argon. In particular, Inventive Example 5has a K_(Kr)/K_(ar) gas adsorption selectivity ratio greater than 8.

Flammability tests were also performed as described herein. Activatedcarbon was obtained from Alfar Aesar (“AAAC”) and was used to prepareall Inventive and Comparative Examples. All flammability tests wereperformed in air at a flow rate of 60 cubic centimeter per minute (60cm³/min) with a heating rate of 20° C./min up to 1200° C. Flammabilitytests are focused on determination of spontaneous ignition temperatures(SIT). The SITs are graphically determined based on the differentialscanning calorimetry (DSC) curves or thermogravimetric analysis (TGA)curves, as discussed below and in “Characterizing the ignition processof activated carbon” by Y. Suzin, et al, Carbon, vol. 37, pp. 335-346(1999).

In the DSC analysis, the SIT is defined as the intersection of thebaseline and the slope at the inflection point of the sample powerdensity (mW/mg) in the plot of power density versus temperature.Similarly, in the TGA, the SIT is defined as the intersection of thebaseline and the slope at the inflection point of the sample mass in theplot of mass change versus temperature. In FIG. 6, the SIT of AAAC isdetermined as 300±10° C. based on the DSC curve. The graphicaldetermination method results in an uncertainty of 10° C. In Table 6, theSITs for Inventive Examples 1-9 as well as for the pure AAAC are listed.As the Inventive Examples have strong endothermic reactions, all SITsfor the Inventive Examples are determined based on the TGA curves. Thebaselines of mass retained are constructed after consideration of masschanges associated with endothermic reactions (See FIGS. 7-15).

Each of the Inventive Examples has much higher SITs in comparison withthe AAAC reference material. For instance, the SIT of inventive Example7 is 560° C. higher than that of AAAC. In addition, a portion of theactivated carbon survives in the Inventive Examples even after heatingto 1200° C., as residual activated carbon was observed after theadvanced forms of activated were heated to 1200° C. Thus, the firehazard is eliminated when using the advanced forms of activated carbonof the invention.

TABLE 6 Spontaneous ignition Samples temperature (SIT),° C. Alfar Aesaractivated carbon 300 ± 10^(A) Inventive Example 1 550 ± 10^(A) InventiveExample 2 600 ± 20^(B) Inventive Example 3 495 ± 15^(B) InventiveExample 4 540 ± 5^(B)  Inventive Example 5 575 ± 8^(B)  InventiveExample 6 595 ± 10^(A) Inventive Example 7 860 ± 10^(A) InventiveExample 8 720 ± 10^(A) Inventive Example 9 650 ± 10^(A) InventiveExample 10 640 ± 10^(A) Inventive Example 11 735 ± 10^(A) InventiveExample 12 400 ± 10^(A) ^(A)Assigned uncertainty based on singledetermination. ^(B)Analytical uncertainty based on replicatedeterminations.

In summary, the Inventive Examples outperform the Comparative Examplesin both adsorption capacities, and kinetics for adsorption of noblegases. Moreover, the Inventive Examples have adsorption capacities andkinetics comparable to those of commercially-available activated carbon.As can be seen by the very high structural ignition temperatures ofTable 6, the inventive use of one or more carbon dioxide-evolvingadditives with, or without, structural water contained in the additivesby the compositions of the Inventive Examples, the Inventive Examples donot pose a fire hazard.

The advanced, fire-resistant forms of activated carbon, according to thepresent invention, have high gas adsorption capacities and rapidadsorption kinetics (comparable to commercially-available activatedcarbon), without having any intrinsic fire hazard.

They also have superior performance to Mordenites in both adsorptioncapacities and kinetics. In addition, the Inventive Examples do not posethe fibrous inhalation hazard that exists with use of Mordenites.

We claim:
 1. An advanced activated carbon composition comprising:between 5 and 95 wt % of one or more hydrated and/orcarbonate-containing mineral; and the balance activated carbon; whereinthe one or more hydrated and/or carbonate-containing mineral containsbetween 10 and 45 wt % water; and wherein the one or more hydratedand/or carbonate-containing mineral is hydrated magnesite.
 2. Thecomposition of claim 1, wherein the one or more hydrated and/orcarbonate-containing mineral is a hydrated magnesite; and wherein thecomposition comprises between 22 and 27 wt % hydrated magnesite and thebalance activated carbon; wherein the hydrated magnesite comprisesbetween 15 and 17 wt % water.
 3. The composition of claim 1, wherein theone or more hydrated and/or carbonate-containing mineral is a hydratedmagnesite; and wherein the composition comprises between 33 and 35 wt %hydrated magnesite and the balance activated carbon; wherein thehydrated magnesite comprises between 15 and 17 wt % water.
 4. Thecomposition of claim 1, wherein the composition has a K_(Kr)/K_(ar) gasadsorption selectivity ratio greater than or equal to
 8. 5. Thecomposition of claim 1, wherein the composition has a spontaneousignition temperature (SIT) greater than or equal to 500° C.